1. Field of the Invention
The present invention relates to a semiconductor Hall element, and more particularly, to a Hall element capable of detecting magnetic fields in vertical and horizontal directions and removing offset voltage.
2. Description of the Related Art
A Hall element enables non-contact position detection and angle detection, and is thus used as a magnetic sensor.
First, the principle of magnetic detection by a Hall element is described. When a magnetic field is applied vertically to a current flowing through a substance, an electric field (Hall voltage) is generated in a direction vertical to both the current and the magnetic field.
FIG. 5 is a diagram for illustrating the principle of an ideal Hall effect. On an ideal Hall element, a Hall voltage VH output from a voltmeter 3 is represented as:VH=μB(W/L)Vdd where W and L represent respectively a width and a length of a Hall element magnetism sensing portion 1, μ represents electron mobility, Vdd represents a voltage applied by a power supply 2 for supplying a current, and B represents an applied magnetic field. A coefficient proportional to the applied magnetic field B corresponds to the magnetic sensitivity, and hence a magnetic sensitivity Kh of this Hall element is represented as:Kh=μ(W/L)Vdd 
As such a Hall element, there have been known a horizontal Hall element configured to detect a magnetic field component vertical to a substrate (wafer) surface and a vertical Hall element configured to detect a magnetic field component horizontal to the substrate surface.
When both of a vertical direction magnetic field and a horizontal direction magnetic field are to be detected, in many cases, the horizontal Hall element and the vertical Hall element are separately formed on the same substrate (wafer) to realize the detection.
On the other hand, in an actual Hall element, an output voltage is generated even when no magnetic field is applied. The voltage output under a magnetic field of zero is called offset voltage. It is considered that the offset voltage is generated when potential distribution inside the element becomes imbalanced by, for example, mechanical stress applied to the element from the outside or misalignment occurring in a manufacturing process. For an actual application, compensation is necessary for the offset voltage so that the offset voltage may be considered to be 0.
Taking a case of a horizontal Hall element as an example, a method of compensating for offset voltage is described.
FIG. 6 is a circuit diagram for illustrating the principle of an offset cancellation circuit utilizing spinning current. A Hall element 10 has a symmetrical shape and includes four terminals T1, T2, T3, and T4 so that a control current is caused to flow between one pair of input terminals and an output voltage is obtained between the other pair of output terminals. When one pair of the terminals T1 and T2 of the Hall element serve as control current input terminals, the other pair of the terminals T3 and T4 serve as Hall voltage output terminals. In this case, when a voltage Vin is applied to the input terminals, an output voltage Vh+Vos is generated between the output terminals, where Vh represents a Hall voltage proportional to a magnetic field of the Hall element and Vos represents an offset voltage. Next, with the terminals T3 and T4 serving as the control current input terminals and the terminals T1 and T2 serving as the Hall voltage output terminals, the input voltage Vin is applied between the terminals T3 and T4 to generate a voltage −Vh+Vos between the output terminals. Reference symbols S1 to S4 denote sensor terminal switching means, and one of terminals N1 and N2 is chosen by a switching signal generator 11.
By subtracting one output voltage from the other which are obtained by the currents flowing in two directions described above, the offset voltage Vos may be cancelled to obtain an output voltage 2Vh proportional to the magnetic field (see, for example, Japanese Patent Application Laid-open No. Hei 06-186103).
Further, offset voltage can be removed by causing current to flow in two directions or more for an offset voltage of a vertical Hall element, or calculating outputs of a plurality of Hall elements (for example, see Japanese Patent Application Laid-open No. 2007-212435).
In order to detect a vertical magnetic field component (Z direction) and horizontal magnetic field components (X and Y directions) on a substrate (wafer) surface, it is necessary to form a horizontal Hall element and a vertical Hall element on the same substrate, which leads to an increase in chip size. Further, a vertical magnetic field and a horizontal magnetic field are detected by separate Hall elements, and hence the magnetic fields are measured at the centers of the respective Hall elements. Thus, the magnetic field components are detected at different positions and accuracy is lost. In addition, in order to compensate for an offset voltage of the vertical Hall element configured to detect a horizontal magnetic field, it is necessary to arrange a plurality of vertical Hall elements, which leads to drawbacks such as a further increase in chip size and a higher cost.